Soil Catena Sequences and Fire Ecology in the Boreal Forest of Alaska

Abstract

This paper is the first to provide chemical, physical, and morphological properties of the soils in the boreal region of Alaska and to demonstrate the dominant effect of landscape attributes in soil formation. This study was conducted to characterize soils and landscape relationships in the boreal forest of Alaska. Sites representing major landform positions and vegetation communities were selected for study. Well‐drained, shallow to moderately deep Inceptisols occur on the drier and warmer south aspect slopes with thin (5–9 cm) organic horizons and loamy textures. Poorly drained Gelisols form on wet and cold north aspect slopes and valley floors with thick (18–52 cm) organic horizons and permafrost within 45 to 60 cm of the surface. On the latter, mineral horizons are reduced. Soils on the ridgetop show features of relic, nonsorted circle (a type of pattern grounds) that indicate a previous periglacial environment. The mineral soil on backslopes is shallow to moderately deep due to gelifluction and slope movement but deep toward toeslopes. Charcoal particles, commonly found within the soil profiles, attest to frequent fire events in the past. Fire has the greatest impact on soil properties on south aspect slopes because the organic horizons are thin and dry, and easily destroyed by fire. The underlying mineral horizons often develop hydrophobicity resulted from moderately and severe burn. Slope, aspect, and slope gradient are major controlling factors for the contrasting soil types along the catena sequences in the watershed.